Dock levelers are mounted on a loading dock and are adapted to span the gap between the loading dock and the bed of a carrier or truck parked in front of the dock so that material handling equipment, such as a lift truck, can move conveniently between the dock and the truck bed.
One common form of dock leveler is mounted in a pit or recess formed in the dock surface and includes a ramp or deck plate which is stored in a generally horizontal position flush with the upper surface of the dock and is movable to an upwardly inclined position. A lip is hinged to the forward edge of the ramp and can be pivoted between a downwardly hanging pendant position, and an extended position where the lip forms an extension to the ramp.
Another form of dock leveler is a type known as an edge-of-dock leveler which is mounted to the front surface of the dock and thus does not require a preformed pit in the dock and can be utilized with existing docks. The conventional edge-of dock leveler includes a deck plate which is hinged to the frame of the leveler and a lip is pivotally connected to the forward edge of the deck plate. In the storage position, the deck plate is generally horizontal and the lip hangs downwardly in the pendant position. To move the leveler to an operating position, the deck plate is pivoted upwardly to a generally vertical position thus elevating the lip to a position above dock level, and the deck plate and lip are then moved forwardly to enable the lip to engage the bed of the truck.
In the past, the typical edge-of-dock leveler has been operated manually. For example, an operator, standing on the dock and using a long hook-like implement, engages the deck plate and pivots the deck plate upwardly to the vertical position. The lip is then engaged by the implement and pivoted to the extended vertical position, and the leveler is then lowered to bring the extended lip into engagement with the truck bed. Because of the weight of the deck plate and the lip, it is very difficult to manually pivot the deck plate and the lip upwardly to the vertical position.
To facilitate the lifting of the deck plate and the lip to the vertical position, it has been proposed to incorporate a counterbalancing mechanism. Not only is a counterbalancing mechanism expensive, adding to the cost of the unit, but the counterbalancing mechanism exerts an upward force on the deck plate and may tend to prevent firm contact between the lip and the truck bed, particularly when a fork lift truck, or other load, jars the deck plate, as the fork lift truck moves across the deck plate.
It has also been proposed to utilize a hydraulic system to move the deck plate and lip of the edge of dock leveler to the upper or vertical position. In a typical hydraulic system, a hydraulic cylinder unit is interconnected between the frame of the leveler and the deck plate. However, the use of a hydraulic system substantially increases the overall cost of the leveler.